The present, invention relates to a transmitting system, apparatus, a recording and reproducing apparatus, and a recording apparatus, for transmitting/recording a stream comprising plural packets according to MPEG (Moving Picture Experts Group)2.
It has been well known that a TS (transport stream) according to MPEG2 i , a stream comprising compressed digital video, compressed digital audio, and the like. The TS is used in digital broadcasting, and contains multiplexed plural programs. Hereinafter, xe2x80x9cTSxe2x80x9d always refers to the TS according to MPEG2 (MPEG2 TS). MPEG2 is defined in ITU-T H.222.0 (ISO/IEC 13818-1) xe2x80x9cGeneric Coding of Moving Pictures And Associated Audio Informationxe2x80x9d.
FIGS. 3(a) and 3(b) show the TS. Shown in FIG. 3(a) are TS packets. The TS comprises a set of TS packets which are fixed in length (188 byte). The TS packets each includes plural fields, i.e., 8-bit Sync Byte, a 13-bit PID (Packet identifier), a 4-bit CC (Continuity Counter), an AF (Adaptation Field) (0-184 bytes), and a payload (0-184 bytes), and so forth. Information irrelevant to the present invention is not discussed herein. Information in respective fields of the TS packet will be discussed below.
The Sync Byte (8 bits) is positioned at the head of the TS packet, and is 0x47 (0x: Hexadecimal numeral), which is used for detecting the head of the packet.
The PID (13 bits) is used for identifying payload data. According to plural PIDs, plural programs contained in one TS can be identified PID-0x1fff indicates that the corresponding TS racket is an ineffective (null) packet.
The CC (4 bit) increases ore by one among the TS packets of the same PID. In some cases, neighboring TS packets of the same PID take the same CC value. They are called a xe2x80x9cDuplicated Packetxe2x80x9d. When the Duplicated Packet is transmitted, two TS packets of the same content are sequentially transmitted.
The AF (0-184 bytes) is used for storing additional information.
The Payload (0xe2x88x9d184 bytes) is used for storing actual data, the length of which is determined by the length of the AF.
In addition, the TS contains PCRs (Program Clock References) inserted at regular intervals. The PCR is information which a decoder at a receiving end uses so as to set the value of a reference time STC (System Time Clock) to the value intended by a transmitting end. Therefore, it is required that the PCR arrive at the receiving and at a timing as intended by the transmitting end.
When the TS is used in the digital broadcasting, as shown in FIG. 3(b), an error correction code is some times added after the TS packet. The typical code length of the error correction code is 16 bytes, and the TS packet and the error correction code (204 bytes in total) is transmitted as a unit. In some cases, the error correction code (16 byte) is dummy data.
A description will be given of a prior art transmitting system which transmits the TS described above.
One example of the prior art transmitting system is a system which adopts an adaptive clock system using an ATM (Asynchronous Transfer Mode). This is described in detail in Practical MPEG Text (P218-221), published by Aski Publishing Company
FIG. 8 shows this prior art transmitting system. In FIG. 8, reference numerals 81, 82, 83, 821, 822, and 823 designate a transmitting apparatus, a receiving apparatus, a transmission line, receiving means, storage means, and PLL (phase-locked loop), respectively. The MPEG2 TS is input to the transmitting apparatus 81, the transmitting means 811 which transmits the input data to the transmission line 83. The transmission line 83 is an ATM network. When transmitting input data on the transmission line 83, some variance of delay occurs. The receiving means 821 of the receiving apparatus 82 receives data on the transmission line 83. The receiving means 821 stores the received data in the storage means 822. The storage means 822 is an FIFO (first-in, first-out) memory, and outputs the input data in synchronization with the output clock. The PLL 823 adjusts the speed of the output clock so that the amount of data stored in the storage means 822 is kept constant. To be specific, when the amount of stored data is larger than a predetermined value, the PLL 823 makes the speed of the output clock higher, while when the amount is smaller than the predetermined value, the PLL 823 makes the speed lower.
As described above, in the prior art transmitting system, although some variance of delay occurs on the transmission line 83, the PLL 823 and the storage means 822 of the receiving apparatus 82 make it possible to decode the data correctly
However, in the prior art method, all the packets (programs) contained in the input data are transmitted even for the case where only a part of them needs to be transmitted. This makes it impossible to realize effective use of the band of the transmission line.
The similar problem occurs in the recording and reproducing apparatus.
It is an object of the present invention to provide a transmitting system which is capable of transmitting data in such a manner that data to be transmitted on a transmission line can be reduced and a stream can be reproduced correctly when it is received.
It is another object of the present invention to provide a recording and reproducing apparatus which is capable of recording and reproducing data in such a manner that data to by recorded in a recording medium can be reduced and the stream ran be reproduced correctly when it is reproduced.
Other objects and advantages of the invention will become apparent from the detailed description that follows. The detailed description and specific embodiments described are provided only for illustration since various additions and modifications within the spirit and scope of the invention will be apparent to those skill in the art from the detailed description.
According to a first aspect of the present invention, in a transmitting system which comprises a transmission line, a transmitting apparatus connected to the transmission line, and a receiving apparatus connected to the transmission line, and transmits data between the transmitting apparatus and the receiving apparatus, the transmitting apparatus comprises: packet compressing means which receives input data comprising plural packers having identifiers as an input, identifies packets to be discarded and effective packets according to the identifiers, and outputs compression information indicating the number of continuously discarded packets and the effective packets to the transmission line, and the receiving apparatus comprises: packet restoring means which receives the compression information and the effective packets which have been output from the transmitting apparatus generates ineffective packets which are as many as the discarded packets, and outputs the ineffective packets and the effective packets. Therefore, it is possible to realize a transmitting system which is capable of reducing data to be transmitted on the transmission line and reproducing the stream correctly when it is received.
According to a second aspect of the present invention, in the transmitting system of the first aspect, the transmitting apparatus further comprises: identifying means which receives, a fixed clock and the input data synchronized with the fixed clock as inputs, identifies the packets to be discarded and the effective packets according to the identifiers, and outputs identification signals each indicating that a packet is either the effective, packet or the packet to be discarded; and counting means for counting the number of continuously discarded packets from the identification signals.
According to a third aspect of the present invention, in the transmitting system of the second aspect, the input data to the transmitting apparatus is a transport stream according to MPEG2, and the identification signals each indicates that the packet is either the packet to be discarded or the effective packet according to the corresponding packet identifier.
According to a fourth aspect of the present invention, in the transmitting system of the third aspect, the output means of the transmitting apparatus inserts the compression information for replacing a continuity counter of an effective packet positioned immediately after the compression information, and the packet restoring means of the receiving apparatus uses data in the continuity counter as the number of the continuously discarded packets, and replaces the continuity counter with the number which increases one by one among the packets of the same packet identifier. Therefore, when transmitting TS packets contained in the MPEG2 transport stream, it is possible to further reduce data to be transmitted.
According to a fifth aspect of the present invention, in the transmitting system of the second aspect, the transmitting apparatus, when the value of the counting means reaches a predetermined value, outputs either the packet to be discarded or the ineffective packet into which the discarded packet has been converted, as the effective packet. Therefore, it is possible to make fixed length data of the number of continuously discarded packets
According to a sixth aspect of the present invention, in the transmitting system of the first or second aspect, the receiving apparatus further comprises: a storage for storing the ineffective packets and the effective packets as data and outputting the packets in synchronization with a clock in the order in which the packets are input; and an adaptive clock generating device for outputting the clock so that the amount of the data stored its the storage is kept constant. Therefore, it is possible to reproduce the clock synchronized with the data from the transmitting end.
According to a seventh aspect of the present invention, in the transmitting system of the sixth aspect, the adaptive clock generating device outputs the clock so that the amount of the data stored in the storage when one effective packet is input thereto is kept constant. Therefore, it is possible to reproduce the clock more correctly.
According to an eighth aspect or the present invention, in the transmitting system of the first or second aspect, the receiving apparatus further comprises: a storage for storing the effective packets and the compression information as data and outputting the data in the order as entered; packet restoring means for reading the data from the storage, outputting the ineffective packets when there is no data in the storage and outputting the ineffective packets which are as many as the discarded packets of the number indicated by the compression information and the effective packets when there is data in the storage, the ineffective packets and the effective packets being output in synchronization with the clock; a counter for increasing its value by (the number of the discarded packets indicated by the compression information)xc3x97(packet length) when the compression information is input thereto, increasing its value by the packet length of the effective packet when the effective packet is input thereto, and decreasing its value by one when the clock is input thereto; and an adaptive clock generating device for outputting the clock so that the value of the counter is kept constant. Therefore, it is possible to realize a small-scale circuit including a storage of a smaller capacity.
According to a ninth aspect of the present invention, in the transmitting system of the eighth aspect, the adaptive clock generating device outputs the clock so that the value of the counter counted when the effective packet is received is kept constant Therefore, it is possible to reproduce the clock more correctly.
According to a tenth aspect of the present invention, a transmitting apparatus for processing input data and outputting the processed data to a transmission line, comprises: identifying means which receives a fixed clock and an MPEG2 transport stream as input data comprising plural packets having identifiers as inputs, identifies packets to be discarded and effective packets according to the identifiers, and outputs the effective packets and identification signals each according to a packet identifier of either the packet to be discarded or the effective packet; counting means for counting the number of continuously discarded packets from the identification signals; and output means for outputting compression information indicating the number of continuously discarded packets which has been counted by the counting means and the effective packets to the transmission line.
According to an eleventh aspect of the present invention, in the transmitting apparatus of tenth aspect, the output means inserts the compression information for replacing a continuity counter of the effective packet positioned immediately after the compression information.
According to a twelfth aspect of the present invention, a transmitting apparatus for processing input data and outputting the processed data to a transmission line, comprises: identifying means which receives a fixed clock and the input data comprising plural packets having identifiers which is synchronized with the fixed clock as inputs identifies the packets to be discarded and the effective packets according to the identifiers and outputs identification signals each indicating that a packet is either the effective packet or the packet to be discarded; counting means for counting the number of continuously discarded packets from the identification signals; and output means for outputting compression information indicating the number of continuously discarded packets which has been counted by the counting means and the effective packets to the transmission line; the output means outputting either the discarded packet or the ineffective packet into which the discarded packet has been converted, as the effective packet, when the value of the counting means reaches a predetermined value.
According to a thirteenth aspect of the present invention, in a recording and reproducing apparatus which comprises a recording apparatus for processing input data and recording the processed data in a rrecording medium, and a reproducing apparatus for reading the data from the recording medium, the recording appparatus comprises: identifying means which receives a fixed clock and an MPEG2 transport stream as input data comprising plural packets having identifiers which are synchronized with the fixed clock as inputs, identifies packets to be discarded and effective packets according to the identifiers, and outputs the effective packets and identification signals each according to a packet identifier of either the packet to be discarded or the effective packet; counting means which increases its value by one when the idenfification signal indicates that the packet is the packet to be discarded, and outputs its value as compression information and then sets its value to zero when the identification signal indicates that the packet is the effective packet; and recording means which records the compression information output from the counting means and the effective packets in the recording medium; and the reproducing apparatus comprises: packet restoring means which reads the compression information indicating the number of discarded packets and the effective packets from the recording medium, generates ineffective packets as many as the discarded packets, and outputs the ineffective packets and the effective packets. Therefore, it is possible to realize a recording and reproducing apparatus which is capable of recording data to be recorded in the recording medium and reproducing the streanm more correctly when it is reproduced.
According to a fourteenth aspect of the present invention, in the recording and reproducing apparatus of the thirteenth aspect, the recording means of the recording apparatus inserts the compression information for replacing a continuity counter of an effective packet positioned immediately after the compression information, and the packet restoring means of the receiving apparatus uses data is the continuity counter as the number of the continuously discarded packets, and replaces the continuity counter with the number which increases one by one among the packets of the same packet identifier. Therefore, when recording TS packets contained in the MPEG2 transport stream, it is possible to reduce data to be recorded.
According to a fifteenth aspect of the present invention, in a recording and reproducing apparatus which comprises a recording apparatus for processing input data and recording the processed data in a recording medium, and a reproducing apparatus for reading the data from the recording medium, the recording apparatus comprises: identifying means which receives a fixed clock and input data comprising plural packets having identifiers which are synchronized with the fixed clock as inputs, identifies packets to be discarded and effective packets according to the identifiers, and outputs the effective packets and identification signals each indicating that a packet is either the packet to be discarded or the effective packet; counting means which increases its value by one when the identification signal indicates that the packet is the packet to be discarded, and outputs its value as compression information and then sets its value to zero when the identification signal indicates that the packet is the effective packet; and recording means which records the compression information output from the counting means and the effective packets in the recording medium; the recording means recording either the discarded packet or the ineffective packet into which the discarded packet has been converted, as the effective packet, when the value of the counting means reaches a predetermined value; and the reproducing apparatus comprises: packet restoring means which reads the compression information indicating the number of discarded packets and the effective packets from the recording medium, generates ineffective packets as many as the discarded packets, and outputs the ineffective packets and the effective packets.
According to a sixteenth aspect or the present invention, a recording apparatus for processing input data and recording the processed data in a recording medium, comprises: identifying means which receives a fixed clock and an MPEG2 transport stream as input data comprising plural packets having identifiers which is synchronized with the fixed clock as inputs, identifies packets to be discarded and effective packets according to the identifiers, and outputs the effective packets and identification signals each according to a packet identifier of either the packet to be discarded or the affective packet; counting means which increases its value by one when the identification signal indicates that the packet is the packet to be discarded, and outputs its value as compression information and there sets its value to zero when the identification signal indicates that the packet is the effective packet; and recording means which records the compression information output from the counting means and the effective packets in the recording medium.
According to a seventeenth aspect of the present invention, in the recording apparatus of the sixteenth aspect the recording means of the recording apparatus inserts the compression information for replacing a continuity counter of an effective packet positioned immediately after the compression information.
According to an eighteenth aspect of the present invention, a recording apparatus for processing input data and recording the processed data in a recording medium, comprises: identifying means which receives a fixed clock and input data comprising plural packets having identifiers which are synchronized with the fixed clock as inputs, identifies packets to be discarded and effective packets according to the identifiers, and outputs the effective packets and identification signals each indicating that a packet is either the packet to be discarded or the effective packet; counting means which increases its value by one when the identification signal indicates that the packet is the packet to be discarded, and outputs its value as compression information and then sets its value to zero when the identification signal indicates that the packet is the effective packet; and recording means which records the compression information output from the counting means and the effective packets in the recording medium; the recording means recording either the discarded packet or the ineffective packet into which the discarded packet has been converted as the effective packet, when the value of the counting means reaches a predetermined value.